The employment of thermionic cathode coatings in electron discharge devices is well known. These coatings, as applied to cathode substrates of suitable materials, such as nickel or nickel alloys, generally comprise barium carbonate and one or more of the carbonates of calcium or strontium together with an organic binder to allow the coating to be painted, dipped, sprayed or otherwise applied to a particular area of the cathode substrate. Subsequent processing reduces the carbonates to the oxides and then to the free metals, particularly barium, (which supplies the electrons) and volatilizes and removes the organic binder, this processing being done while the device is on exhaust. While this procedure has been employed for many years it is difficult to always remove all of the binder material, and that which remains results in below normal emission properties for the device.